Cleaning of hollow fibre membranes

Abstract

PCT No. PCT/AU95/00587 Sec. 371 Date Aug. 8, 1997 Sec. 102(e) Date Aug. 8, 1997 PCT Filed Sep. 8, 1995 PCT Pub. No. WO96/07470 PCT Pub. Date Mar. 14, 1996A method and apparatus for recovering fine solids from a liquid feed suspension is disclosed. The apparatus has an operating cycle including a concentration part of the cycle in which solids present in the feed suspension are concentrated and a backwash part of the cycle in which supply of feed suspension to the concentrator is interrupted, the concentrator comprises a shell (11), and a plurality of elastic, hollow, microporous, polymer fibers (12) being fixed at their ends within the shell (11). Pressurized feed suspension is supplied to the outside of the fibers during said concentration part of the cycle and the filtrate may be withdrawn from the fiber lumens during the operating cycle. During the backwash cycle the concentration part of the cycle is terminated by ceasing supply of feed to said exterior surface of the fibers (12). The shell (11) is then sealed and the remaining filtrate removed from the lumens. A source of fluid under pressure is then applied to said lumens before, at the same time as, or just after opening the shell (11) to atmosphere, to cause explosive decompression through the walls of the fibers (12) whereby the fluid under pressure passes through said walls. The pressure level in said lumens is maintained at a predetermined value for a sufficient time following said decompression to cause substantial portions of solids lodged within and/or on the fiber walls to be dislodged. The dislodged contaminant matter is then washed away by the application of a flow of liquid over the surface of the fiber walls; and the concentration part of the operating cycle is recommended by introducing the supply of feed suspension to said exterior surface of said fibers (12).

We claim: 
     
       1. A method of backwashing a plurality of hollow fibres having microporous walls which have been subjected to a filtration operation wherein feed containing contaminant matter is applied to the exterior surface of said hollow fibres and filtrate withdrawn from the ends of the lumens of the fibres, the fibres being contained within a shell or housing, said method comprising: (a) terminating the filtration operation by ceasing supply of feed to said exterior surface of said fibres,   (b) sealing the shell and substantially removing remaining filtrate from said lumens,   (c) applying a source of fluid under pressure to said lumens before, at the same time as, or just after opening the shell to atmosphere, to cause explosive decompression through the walls of the fibres whereby said fluid under pressure passes through said walls;   (d) maintaining the pressure level in said lumens at a predetermined value for a sufficient time following said decompression to cause substantial portions of contaminant matter lodged within and/or on said fibre walls to be dislodged;   (e) washing dislodged contaminant matter away by the application of a flow of feed liquid over the external surface of said fibre walls; and   (f) recommencing the filtration operation by reintroducing said supply of feed to said exterior surface of said fibres while fluid pressure is still being applied to said lumens.   
     
     
       2. A method of backwash according to claim 1 wherein the fibres are rewetted prior to reconnecting the filtration operation. 
     
     
       3. A method of backwashing according to claim 1, wherein during step (c), the lapse time between the start of application of fluid under pressure to the explosive decompression is in the range of about 0.05 seconds to about 5 seconds. 
     
     
       4. A method of backwashing according to claim 3 wherein the fibres are rewetted prior to recommencing the filtration operation. 
     
     
       5. A method of backwashing according to claim 1 wherein feed liquid is reintroduced for a period of between about 1 to about 30 seconds. 
     
     
       6. A method according to claim 1 wherein said fluid pressure exceeds shell side pressure by about 10 kPa to about 800 kPa. 
     
     
       7. A method of backwashing according to claim 1 wherein the pressure applied to said lumens prior to said explosive decompression is between about 100 kPa to about 1200 kPa. 
     
     
       8. A method according to claim 1 wherein during step (b) the filtrate is allowed to drain out of said lumens of its own volition. 
     
     
       9. A method according to claim 1 wherein the steps of the method are curried out as a continuous process utilizing repetitive cycles of solids retention and backwash.